Pressure activated safety valve with grooved membrane

ABSTRACT

A pressure activated valve comprises a valve housing defining a lumen for receiving bodily fluids therein and a flexible membrane disposed in the valve housing. The flexible membrane includes a slit extending therethrough so that the flexible membrane may be moved between an open and a dosed configuration based on fluid pressure within the lumen. A nonthrombogenic coating may be formed on fluid contacting surfaces of the flexible membrane.

The present application incorporates by reference the entire disclosureof U.S. Application entitled “Pressure Activated Safety Valve With HighRow Slit” filed on even day herewith naming Karla Weaver and PaulDiCarlo as inventors, and U.S. Application entitled “Stacked MembraneFor Pressure Actuated Valve” filed on even day herewith naming KarlaWeaver and Paul DiCarlo as inventors, and U.S. Application entitled“Pressure Actuated Safety Valve With Spiral Flow Membrane” filed on evenday herewith naming Paul DiCarlo and Karla Weaver as inventors, and U.S.Application entitled “Dual Well Port Device” filed on even day herewithnaming Katie Daly, Kristian DiMatteo and Eric Houde as inventors.

BACKGROUND OF THE INVENTION

Many medical procedures require repeated and prolonged access to apatient's vascular system. For example, during dialysis treatment bloodmay be removed from the body for external filtering and purification, tomake up for the inability of the patients kidneys to carry out thatfunction. In this process, the patient's venous blood is extracted,processed in a dialysis machine and returned to the patient. Thedialysis machine purifies the blood by diffusing harmful compoundsthrough membranes, and may add to the blood therapeutic agents,nutrients etc., as required before returning it to the patient's body.Typically the blood is extracted from a source vein (e.g., the vanecave) through a catheter sutured to the skin with a distal needle of thecatheter penetrating the source vein.

It is impractical and dangerous to insert and remove the catheter foreach dialysis session. Thus, the needle and catheter are generallyimplanted semi permanently with a distal portion of the assemblyremaining within the patient in contact with the vascular system while aproximal portion of the catheter remains external to the patient's body.The proximal end is sealed after each dialysis session has beencompleted to prevent blood loss and infections. However, even smallamounts of blood oozing into the proximal end of the catheter may bedangerous as thrombi can form therein due to coagulation. These thrombimay then be introduced into the patient's vascular system when bloodflows from the dialysis machine through the catheter in a later session.

A common method of sealing the catheter after a dialysis session is toshut the catheter with a simple clamp. This method is oftenunsatisfactory because the repeated application of the clamp may weakenthe walls of the catheter due to the stress placed on the walls at asingle point. In addition, the pinched area of the catheter may not becompletely sealed allowing air to enter the catheter which may coagulateany blood present within the catheter. Alternatively, valves have beenused at the opening of the catheter in an attempt to prevent leakingthrough the catheter when the dialysis machine is disconnected. However,the unreliability of conventional valves has rendered themunsatisfactory for extended use.

SUMMARY OF THE INVENTION

In one aspect, the present invention is directed to a pressure activatedvalve comprising a valve housing defining a lumen for receiving bodilyfluids therein and a flexible membrane disposed in the valve housing.The flexible membrane includes a slit extending therethrough so that theflexible membrane may be moved between an open and a closedconfiguration based on fluid pressure within the lumen. Anonthrombogenic coating is formed on fluid contacting surfaces of theflexible membrane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a central line catheter according to anembodiment of the present invention;

FIG. 2 is a diagram showing a cutaway view of a pressure activated valveaccording to an embodiment of the present invention, in openconfiguration when a fluid is being introduced;

FIG. 3 is a diagram showing a cutaway view of the pressure activatedvalve according to an embodiment of the present invention, in closedconfiguration;

FIG. 4 is a diagram showing a cutaway view of the pressure activatedvalve according to an embodiment of the present invention, in openconfiguration when the fluid is being withdrawn;

FIG. 5 is a diagram showing a silicone disk forming an openable elementof a pressure activated valve according to an embodiment of the presentinvention;

FIG. 6 is a diagram showing a silicone disk having a V-shaped slitforming an openable element of a pressure activated valve according toan embodiment of the present invention;

FIG. 7 is a diagram showing a silicone disk having a H-shaped slitforming an openable element of a pressure activated valve according toan embodiment of the present invention;

FIG. 8 is a diagram showing a silicone disk having a S-shaped slitforming an openable element of a pressure activated valve according toan embodiment of the present invention;

FIG. 9 is a diagram showing a silicone disk having a radially shapedslit forming an openable element of a pressure activated valve accordingto an embodiment of the present invention;

FIG. 10 is a diagram showing a silicone disk having a plurality of slitsforming an openable element of a pressure activated valve according toan embodiment of the present invention; and

FIG. 11 is a diagram showing three silicone disks forming an openableelement of a pressure activated valve according to an embodiment of thepresent invention.

DETAILED DESCRIPTION

The present invention may be further understood with reference to thefollowing description and the appended drawings, wherein like elementsare referred to with the same reference numerals. The present inventionis related to medical devices used to access the vascular system of apatient, and in particular to central line catheters used for chronicaccess to a vein or artery.

Semi-permanently placed catheters may be useful for a variety of medicalprocedures which require repeated access to a patient's vascular systemin addition to the dialysis treatments mentioned above. For example,chemotherapy infusions may be repeated several times a week for extendedperiods of time. For safety reasons, as well as to improve the comfortof the patient, injections of these therapeutic agents may be bettercarried out with an implantable, semi-permanent vascular accesscatheter. Many other conditions that require chronic venous supply oftherapeutic agents, nutrients, blood products or other fluids to thepatient may also benefit from implantable access catheters, to avoidrepeated insertion of a needle into the patients blood vessels. Thus,although the following description focuses on dialysis, those skilled inthe art will understand that the invention may be used in conjunctionwith any of a wide variety of procedures which require long termimplantation of catheters within the body.

Examples of such implantable catheters include those manufactured byVaxcel™, such as the Chronic Dialysis Catheter and the ImplantableVascular Access System. These devices typically are inserted under thepatient's skin, and have a distal end which includes a needle used toenter a blood vessel. The devices also have a proximal end extendingoutside the body for connection with an outside line. Thesesemi-permanent catheters may be sutured to the patients skin to maintainthem in place while the patient goes about his or her normaloccupations.

FIG. 1 shows an exemplary catheter such as, for example, the Vaxcel™Chronic Dialysis Catheter. The catheter 10 has a distal end 12 that isinsertable into a patient's vein, and which remains within the patient'sbody for the life of the catheter 10. The distal end 12 includes aneedle (not shown) that pierces the vein of the patient to reach theflow of blood. During dialysis, blood from the patient is removedthrough the catheter 10, and is purified by a dialysis machine (notshown) which is connected to a hub 18 of the catheter 10 via an externalline 20. The catheter 10 may include two or more lumens with a first oneof the lumens being used to remove blood from the blood vessel and asecond one of the lumens being used to reintroduced treated blood and/ortherapeutic agents into the blood vessel. As described above, inaddition to dialysis, devices similar to the catheter 10 may be used toaccess a patient's vascular system for other types of treatment, forexample to infuse chemotherapy agents or other medications, to supplyfood and to remove blood samples.

When disconnected from the dialysis machine, the catheter 10 remainswithin the patient, connected to the patients vascular system. Thus, itis important to securely seal the hub 18 to prevent fluids from escapingtherefrom and contaminants from entering the patients body. For example,although the proximal end of the catheter 10 may be clamped to close itoff, if an effective seal is not obtained, the patient runs a serious ofinfection as well as risks of embolisms due to air entering the bloodstream and venous thrombosis due to coagulation of blood in and near thecatheter. In addition, leakage from an improperly sealed catheter mayexpose attending medical staff to a risk of infection by blood bornepathogens. Thus a mechanism is necessary to ensure that the catheter 10is sealed when not in use.

Conventional clamps or clips have been used to seal such catheters 10between medical sessions. However, as the sealing forces repeatedlyapplied by these clips is exerted on a small portion of the surface areaof the catheter 10, damage to the wall of the catheter 10 at thisportion can significantly reduce the effective life of the catheter 10.It is also desired to improve the resistance of a sealing mechanism forthe catheter 10 to forces applied during activities of the patient, sothat the sealing mechanism will remain effective without restricting theactivity of the patient. Finally, it is desired to minimize the bulk ofthe sealing mechanism to enhance patient comfort.

An alternative to clamping or clipping the catheter 10 is to includeself sealing valves near the entrance of the flow passages of thecatheter, to seal those passages when not in use. For example, the hub18 may house one or more valves 22 which are designed to seal thelumen(s) of the catheter 10 under certain conditions, and to allowpassage of fluid therethrough under other conditions. In an exemplarycase applicable to a dialysis catheter, the system of valves may sealthe catheter 10 when it is not connected to an operating dialysismachine, and may allow both an outflow of non-purified blood and aninflow of purified blood to the patient when an operating dialysismachine is connected thereto. These valves 22 thus selectively allowflow into or out of the patient depending on whether they are placed influid contact with the inflow or outflow portions of the dialysiscatheter.

Pressure activated safety valves (PASV's) are one type of flow controldevice that has been used to seal vascular catheters when not in use.These valves open when subject to flow pressure of at least apre-determined value and remain closed when subject to pressures belowthe pre-determined value. In the exemplary case of a PASV used in adialysis catheter, the valve is preferably designed so that thepre-determined pressure substantially exceeds a pressure to which thevalve would be subjected from the vascular system or due to patientactivity and may correspond to a pressure approximating a lower level ofthe pressures to which the valve would be subjected by an operatingdialysis machine. Thus, when no dialysis machine is connected to thecatheter, the pressure in the lumen is insufficient to open the PASV,and the catheter remains sealed.

FIGS. 2-4 show a more detailed view of a PASV 22, shown in a cutawaydrawing depicting three flow conditions in a single lumen catheter 10which handles blood flow from and to the patient's vascular system. FIG.2 shows PASV 22 as a fluid is being introduced into the catheter 10 fromthe hub 18. FIG. 3 shows the valve is closed and no flow is present, andFIG. 4 shows PASV 22 as fluid is being removed from the catheter 10 tothe hub 18, and. In the context of a dialysis catheter, FIGS. 2 and 4,respectively, correspond to blood being returned to and withdrawn from apatient while FIG. 3 corresponds to a condition in which no dialysistreatment is being performed and the PASV 22 is in the sealedconfiguration. According to one exemplary embodiment of the presentinvention, the PASV 22 comprises a valve housing 30 forming a body ofthe device and a slitted membrane 32 disposed within the housing 30. Thehub 18 may define the valve housing 30 or, alternatively, the housing 30and the hub 18 may be separate units. The housing 30 defines a flowchamber 36 through which the fluid flows into and out of the catheter10. The exemplary flow chamber 36 is substantially cylindrical. However,those skilled in the art will understand that, for differentapplications, the flow chamber 36 may be of any shape suitable for theefficient flow of a fluid therethrough.

The slitted membrane 32 may be disposed at any point within the catheter10. However, for purposes of illustration, the membrane 32 is describedas positioned at one end of the flow chamber 36 positioned toselectively impede the passage of fluid therethough. As shown moreclearly in FIG. 5, a slit 34 is formed in the membrane 32 so that underpre-determined conditions the slit 34 opens to allow fluid flow throughthe membrane 32. When the pre-determined conditions are not present, theslit 34 remains closed to prevent fluid flow therethrough. For example,as described above, the sidled membrane 32 may be constructed so thatthe slit 34 opens when subject to a flow pressure of at least apredetermined magnitude, but remains securely closed at other times.According to embodiments of the invention, the PASV 22 includes aslitted membrane 32 that is movable to an open configuration in responseto a predetermined flow pressure, and is biased into the closedconfiguration at all times while the flow pressure remains below thepredetermined flow pressure. The slitted membrane 32 may be formed, forexample, from silicone or from any of a variety of polymer compounds.

FIGS. 2-4 show one exemplary embodiment of a pressure activated valveaccording to the present invention. Those of skill in the art willunderstand that different configurations of the housing 30, the sitedmembrane 32 and the slit 34 may be used without departing from theinvention. For example, as shown in FIGS. 6-9 and discussed in moredetail below, one or more differently shaped slits of various sizes maybe employed, to tailor the flow through the membrane 32 and to vary thepressure required to open the slit 34. Furthermore, the membrane 32 mayhave a different shape and may be located at any place within thehousing 30. The housing 30 may also define a flow chamber 36 having adifferent shape than the substantially cylindrical chamber shown inFIGS. 2-4 with the shape of the membrane 32 being modified to suit thecross-section of the area at which it is to be mounted. For example, themembranes of FIGS. 5-10 are depicted as substantially elliptical.However, those skilled in the art will understand that a flow chamberand membranes of any shape may be employed to achieve desired flowcharacteristics through the catheter 10.

FIG. 6 shows a membrane 32 that is substantially elliptical with a firstslit 52 extending along a major axis thereof. In addition, a pair ofslits 53 is disposed at each end of the slit 52 with the slits 53 ofeach pair extending away from the slit 53 at an angle relative theretoalong lines which converge near the end points of the slit 52. The endsof the slits 53 may be separated from the corresponding end of the slit52 by a distance selected to enhance the structural integrity of themembrane 32 and to increase the threshold pressure to a desired level.However, those skilled in the art will understand that the slits 53 mayintersect the slit 52 in order to achieve desired flow characteristicsso long as the strength of the membrane 32 is maintained at a levelsufficient to withstand the conditions to which it is to be subjected.

FIG. 7 shows substantially elliptical slitted membrane 32 with anH-shaped configuration of slits 54, 55. The slit 54 extendssubstantially along a major axis of the membrane 32 with the slits 65extending substantially perpendicular thereto and separated from ends ofthe slit 54. As described above, the slits 54 and 55 may intersect ifnecessary to achieve the desired flow characteristics of the membrane 32so long as the structural integrity of the membrane 32 is notcompromised. Of course, those skilled in the art will understand thatthe shape of the membrane 32 does not influence the arrangement of theslits formed therein except to the extent that ends of the slits mayneed to be separated from an outer edge of the membrane 32 by a distancesufficient to maintain the strength of the membrane 32.

FIG. 8 shows another embodiment of a slitted membrane 32 with asubstantially S-shaped slit 56 which preferably extends substantiallyalong a center line thereof. For example, if the slitted membrane 32 issubstantially elliptical then the S-shaped slit will oscillate about themajor axis thereof. FIG. 9 shows a membrane 32 including a curved slit58. The curved slit 58 may have any shape and radius of curvaturenecessary to achieve desired flow characteristics of the membrane 32.

Furthermore, the membrane 32 may include a plurality of curved slits 58as shown in FIG. 10. FIG. 10 shows a slitted membrane 32 including fourcurved slits 58 a-58 d with slits 58 a and 58 b positioned on one sideof a major axis of the membrane 32 and slits 58 c and 58 d located on anopposite side thereof. Those skilled in the art will understand thatFIG. 10 shows only one an exemplary embodiment of a slitted membrane 32including a plurality of slits 58 and that a membrane 32 according tothe present invention may include any number of slits 58, which may beof any shape and/or size depending on the flow control requirements ofthe PASV 22.

FIG. 11 shows a membrane 33 formed of three slitted membranes 32 a-32 cstacked on one another. The membrane 33 may be positioned in the flowchamber 36 in, a manner substantially similar to that described abovefor the membranes 32 in order to provide flow control in the PASV 22.Stacking multiple membranes 32 a-32 c provides greater flexibility andtensile strength to the PASV 22 and any number of membranes may bestacked to form such a membrane 33. Those skilled in the art willunderstand that the stilled membrane 32 a has a first slit 34 a formedtherein in any manner as described above and the slitted membrane 32 bhas a first slit 34 b formed therein while the slitted membrane 32 chas, a first slit 34 e formed therein. Each of the stilted membranes 32a-32 e may have more slits formed therein and these additional slitswill preferably align with one another, so that continuous flow pathsare formed through the membrane 33. In addition, these slits 34 a-34 cmay be of different shapes and do not have to match the size and shapeof adjacent slits. For example, the slit(s) 34 a in the membrane 32 amay be substantially S-shaped, while the slit 34 b in the membrane 32 bmay be substantially linear. In addition, one or more of the membranes32 a-32 c may have multiple slits as described above. Furthermore, theslitted membranes 32 a-32 c do not have to be made of the same materialnor do the membranes 32 a-32 c need to have uniform dimensions (e.g.,thickness). This versatility allows PASV 22 to be designed aroundspecific flow control needs. While FIG. 11 shows a membrane 33comprising three slitted membranes 32 a-32 c, one skilled in the artwill understand that any number of slitted membranes may be used,depending on the flow control requirements of the PASV 22.

Furthermore, the slitted membranes 32 a and 32 c that form outersurfaces of the membrane 33 may be beveled by creating grooves 50 a and50 c on surfaces 44 a and 44 c, respectively to direct fluid flow towardthe slits 34 a-34 c which are generally centrally located. In the caseof single membranes 32, creating grooves or reducing the thickness ofportions thereof may undesirably reduce the strength thereof. However,the multiple slitted membranes 32 a-32 c of the membrane 33 provideadditional strength despite the reduced thickness portions resultingfrom the reduced thickness of the membranes 32 a and 32 c.

Whenever a foreign object is placed in contact with the flow of blood,and to a certain extent with other bodily fluids, there is a possibilitythat an occlusion will be formed due to the deposition of cells presentin the blood or other bodily fluid which may present health risks wellknown to those skilled in the art. For example, in the case of a PASV 22in a lumen fluidly coupled to a blood vessel, a fibrin occlusion or clotmay form on a surface of the PASV 22 and/or on the face of a slittedmembrane 32 thereof.

The materials used to construct modern medical devices such as the PASV22 and the slitted membrane 32 are usually synthetic. Thus, when thesematerials come in contact with blood, various reactions such as plateletattachment and platelet activation may be activated that eventuallyprogress to the production of fibrin and to the formation of a clot. Theflow pattern within a valve such as PASV 22 may also to promote theformation of clots. That is as the blood flowing through the PASV 22 andacross the slit is slowed down and redirected by the obstructionpresented by the slitted membrane 32 areas of flow recirculation andstagnation may be formed within the PASV 22. These flow conditions maypromote the formation of thrombi (clots), which may remain within thePASV 22 or which may enter the vascular system.

Coagulation of blood in catheters has been treated by administering tothe patient systemic anticoagulants, such as injectable heparin andwarfarin. However, this approach risks complications due to the possibleintolerance of the patient to those drugs. In addition, in procedureswhen the devices remain in the patients body for extended periods oftime, continuous administration of anti coagulant medications may not bepractical.

According to embodiments of the present invention, a PASV 22 isdescribed which minimizes the formation of clots and/or occlusions inand around the PASV 22. The catheter 10 according to the presentinvention includes a nonthrombogenic coating over surfaces of the devicein the vicinity of the PASV 22 as well as on the surfaces of the PASV 22itself. In particular, a nonthrombogenic coating is applied to innersurfaces of the housing 30 including the lumen walls 40 and end walls 42thereof. In addition, a flexible nonthrombogenic coating may be appliedto the surfaces 44 of the slitted membrane 32 that contact blood orother bodily fluids.

Different nonthrombogenic compounds may be used to coat the surfaces ofinterest. For example, heparin, hydrogel alone or combined with heparin,and phosphorylcholine may be processed to form a coating on the PASV 22and the adjacent inner surfaces of the housing 30. As would beunderstood by those skilled in the art, hydrogels are compounds used todress incisions and to coat medical devices to facilitate theirinsertion into a body cavity. In addition to their lubricatingproperties, hydrogels also exhibit anticoagulant properties. It has beenobserved that a coating of hydrogel disposed on a medical device resultsin a significant reduction in the attachment and activation of plateletsto the device's surfaces. This may be due to the low friction surfacepresented by the coating. Accordingly, the surface concentration ofplatelets may be lower on the surfaces of a PASV valve coated withhydrogel as compared to an untreated valve.

Heparin which has typically been used as an anti-coagulant agentinjected directly into a patient's blood stream may also be used to forma biologically active coating on the surfaces of the PASV 22 whichcontact blood or on the surfaces of the housing 30 adjacent thereto.This type of biologically active coating may be more effective than acoating such as hydrogel, which simply reduces mechanical frictionbetween the device's surfaces and the blood molecules as heparinprevents platelets from adhering to surfaces by interfering with theactivation of various enzymes that otherwise result in the formation offibrin and in the subsequent clotting of blood.

Similarly to heparin, coatings containing phosphorylcholine can beapplied to medical devices such as the valves of a catheter to form abiologically active coating which reduces the formation of surfaceclots. Phosphorylcholine inhibits the adsorption of proteins and reducesadhesion and activation of platelets to the surface of syntheticmaterials. It is thus also an effective agent which may be applied todevices where it is critical to minimize the formation of clots.Additional biologically active compounds may be used to form a coatingon the surfaces of valve housing 30 and sided membrane 32 which are incontact with blood.

In an exemplary embodiment, the coatings applied to the surfaces 44 ofthe slitted membrane 32 are preferably flexible and are designed toadhere thereto and remain in place on these surfaces. Those skilled inthe art will understand that, if the housing 30 is made flexible, thecoatings applied to the inner surfaces 40, 42 of the lumen of thehousing 30 may also require a certain degree of flexibility to accountfor bending of the housing 30 during use and during activity of thepatient. However, the coating on the surfaces 44 of the slitted membrane32 will be subject to more significant stress and strain as the slittedmembrane 32 is repeatedly moved between the open and closedconfigurations during use. In any case, for both the surfaces 40, 42 and44, a coating including a polymer which is able to retain a therapeuticcompound therein may be used. The ability of the nonthrombogenic coatingto remain in place without flaking, cracking or otherwise losing itsintegrity is important since any loose pieces of the coating may travelinto the vascular system. In addition, damage to the coating couldexpose the valve's surfaces to the flow of blood, and increase theprobability that blood clots will form thereon. Those skilled in the artwill understand that known methods may be used to form a flexiblecoating on components of the pressure activated PASV 22, so that thecoating retains its flexibility and integrity over the life of thevalve.

The present invention has been described with reference to specificembodiments, more specifically to a pressure activated safety valve usedin a dialysis catheter. However, other embodiments may be devised thatare applicable to other medical devices, without departing from thescope of the invention. Accordingly, various modifications and changesmay be made to the embodiments without departing from the broadestspirit and scope of the present invention as set forth in the claimsthat follow. The specification and drawings are accordingly to beregarded in an illustrative rather than restrictive sense.

What is claimed is:
 1. A method for infusing fluid to a target sitewithin a human body, the method comprising: providing a vascular accesscatheter comprising a pressure activated valve, the pressure activatedvalve comprising: a valve housing defining a lumen, a flexible membranedisposed in the valve housing, the flexible membrane having asubstantially elliptical disk shape, the flexible membrane comprising: afirst surface and a second surface, a first slit extending through theflexible membrane so that the flexible membrane may be moved between anopen and closed configuration in response to a fluid pressure within thelumen, and a first groove disposed in the first surface, wherein thefirst slit is disposed at least partially within the first groove todirect fluid flow towards the first slit; and infusing fluid through thepressure activated valve and to the target site.
 2. The method of claim1, wherein the flexible membrane further comprises: a second groovedisposed in the second surface, wherein the first slit is disposed atleast partially within the second groove to direct fluid flow towardsthe first slit.
 3. The method of claim 1, wherein the flexible membranefurther comprises: a second slit extending through the flexiblemembrane.
 4. The method of claim 3, wherein the first and second slitstraverse a short axis of the flexible membrane.
 5. The method of claim3, wherein the first and second slits are substantially linear.
 6. Themethod of claim 3, wherein the second slit is substantially parallel tothe first slit.
 7. The method of claim 3, wherein the first and secondslits are different sizes.
 8. The method of claim 3, wherein theflexible membrane further comprises: a third slit extending through theflexible membrane.
 9. The method of claim 8, wherein the first, secondand third slits traverse a short axis of the flexible membrane.
 10. Themethod of claim 8, wherein the first, second and third slits aresubstantially linear.
 11. The method of claim 8, wherein the second andthird slits are disposed in the flexible membrane on opposite sides ofthe first slit.
 12. The method of claim 8, wherein the second and thirdslits are substantially parallel to the first slit.
 13. The method ofclaim 8, wherein at least two of the first, second and third slits aredifferent sizes.